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Thermal Mass for Wood Stove

 
Posts: 14
Location: Upstate NY
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First time poster, long time reader.

We heat with a traditional wood stove, a Drolet HT 1200. It is undersized for our square footage, but we make do. I'd love to build a rocket Mass heater, but realistically it won't happen for a number of reasons. I'd like to add some Mass around the wood stove as a compromise. I'll post a few pics of the set up, and welcome specific suggestions.

Some questions I have:
Should I buy a newer more efficient stove first?Will adding thermal mass sacrifice radiant heat?Can I "cob" around the base, maybe up the sides and back a bit?  Should I cob right up to the metal or leave an air space? If so, how much? What do you think about cobbing in water reservoirs on either side - for example cobbing in a stainless steel pot on each side that could be filled with water for humidity and thermal mass?
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gardener
Posts: 3749
Location: latitude 47 N.W. montana zone 6A
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Hi Gabe;   Welcome to Permies!
Sure you can put mass around your stove to help hold the heat.
I suggest stacking clay brick on 3 sides , as thick and tall as you like. Mortared or dry stack.  Flat stone would work as well.
Water tanks on the sides are also a good mass.

I don't recommend cob on your stove in that nice clean area.  With a metal stove it will constantly be cracking / dusting and generally making a mess.

Next, can you tell me why a rmh is not in the future?  I suspect it could be the insurance thing.  If it is a space / size / weight issue, then there are options these days.
 
Gabe Smith
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thomas rubino wrote:Hi Gabe;   Welcome to Permies!
Sure you can put mass around your stove to help hold the heat.
I suggest stacking clay brick on 3 sides , as thick and tall as you like. Mortared or dry stack...




Thanks for the welcome and the quick reply! Thanks for the tip on the cob also. A rmh is not really a possibility given insurance (actually the least of my concerns given my disdain for rules), space, too many projects, and living in a democratic household (the main reason). Realistically, would standard red brick have decent thermal mass? Another option is we have 300 year old rock walls surrounding our several acres that I could incorporate into a mass surrounding the stove. I guess if I went with that I would need to mortar given they are mostly round/odd shaped. Would field stone crack?
 
gardener
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Location: Westbridge, BC, Canada
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building solar woodworking rocket stoves wood heat greening the desert
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Hi Gabe,   Your metal woodstove was designed to mostly radiate heat away from it - This is so that the metal stays intact without prematurely breaking down or warping. If you were to add too much mass right up against the stove this may happen. Capturing the radiant heat with a gap though is a great idea, but a rocket mass heater would be even more great! Lots of rocket scientists to help you out here :D
 
Gabe Smith
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Gerry Parent wrote:Hi Gabe,   Your metal woodstove was designed to mostly radiate heat away from it - This is so that the metal stays intact without prematurely breaking down or warping. If you were to add too much mass right up against the stove this may happen. Capturing the radiant heat with a gap though is a great idea, but a rocket mass heater would be even more great! Lots of rocket scientists to help you out here :D



Good info, thanks!
 
thomas rubino
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Hi Gabe;
I second Gerry in leaving a gap between the stove and mass. It would warp.
Yes, red clay bricks definitely have enough mass.
They are used in masonry stoves and more important in a rocket mass heater that utilizes a vertical brick bell. Has a smaller foot print to fit odd spaces and significantly less weight.  Add in a batch box style burner and you end up with a gorgeous masonry stove that you burn 2 times a day ... No exposed flames & using heaps less wood than you currently use...
just sayin...

If your interested, check out this site  http://batchrocket.eu/en/ that is the foremost batch box site available.

If your lucky you might just sway the democratic opinion in your house.
If not, its just good information to have.
 
Gabe Smith
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thomas rubino wrote:Hi Gabe;
I second Gerry in leaving a gap between the stove and mass...



Thanks - valuable info! I've read extensively on rmh's and masonry stoves. Perhaps someday...

I started adding some mass today by dry stacking field stone. I figured it would be good permaculture practice to utilize what is available on site rather than purchase something. Since they are all awkward shapes, it's hard to get very high without it being unstable, so I'll have to tool around with it. It takes a while to haul rocks to the house in the snow! I'm also a little worried about the weight. The last thing I want is for the floor to cave in taking firing hot stove with it and burn the house to the ground. Any suggestions about how to sure up floor joists?

I'll post a photo after I get some more mass on...
 
Gerry Parent
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After you get the floor taken care of, you could consider something like a gabion to contain the rocks.
 
pollinator
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Location: North central Ontario
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Hi gabe. I see an eco fan on top do you have a hole in the back cowling for a blower? You will get significant increases of heat off the stove with it. If not get a box fan and mount it behind it on low. Push that heat at the drywall walls and let them act as your mass...
 
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what's the main problem with your existing stove?  Just the daily temperature swings?  How long does a load of dry firewood last?  What sort of high and low temperature do you see in the stove room throughout the day?

How many cords of wood do you burn in a typical winter?

There are efficient catalytic and secondary-burn stoves that even out the temperature swings.  They're not cheap.  I load my Blaze King 2x a day all winter long (3x a day if the night drops into single-digits).  It keeps the house between 65-72 degrees 24/7.  I burn 3-4 cords of hardwood most winters.

The cheapest long-term solution is to improve the insulation and air-sealing of the house. There's a lot of low-hanging fruit for improvement in most cold-climate houses.  
 
Gabe Smith
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Gerry Parent wrote:After you get the floor taken care of, you could consider something like a gabion to contain the rocks.



Good idea
 
Gabe Smith
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David Baillie wrote:Hi gabe. I see an eco fan on top do you have a hole in the back cowling for a blower? You will get significant increases of heat off the stove with it. If not get a box fan and mount it behind it on low. Push that heat at the drywall walls and let them act as your mass...



I do the box fan already. There is a port for a blower, but I haven't installed one since the box fan does the trick when needed.
 
Gabe Smith
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Davis Tyler wrote:what's the main problem with your existing stove?  Just the daily temperature swings?  How long does a load of dry firewood last?  What sort of high and low temperature do you see in the stove room throughout the day?

How many cords of wood do you burn in a typical winter?

There are efficient catalytic and secondary-burn stoves that even out the temperature swings.  They're not cheap.  I load my Blaze King 2x a day all winter long (3x a day if the night drops into single-digits).  It keeps the house between 65-72 degrees 24/7.  I burn 3-4 cords of hardwood most winters.

The cheapest long-term solution is to improve the insulation and air-sealing of the house. There's a lot of low-hanging fruit for improvement in most cold-climate houses.  



The main problem is the stove only has about 35k btu output when realistically I need double that at least. It struggles to heat the house when it is less than 20, which in upstate NY is quite often in the winter. I burn about 3-4 cords as well, harvested from the property, majority deadfall or standing dead. I also started coppicing/pollarding this year on 2 wooded acres that is former grazing land. I want to reduce wood consumption as much as possible. The stove is circa 2000, so has no secondary burn tube or anything. I definitely need a more efficient stove. But I prefer to buy second hand, so they are hard to come by. I might have to pay the money though.
 
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Good evening . Do you know the temperature of smoke in chimney ? It is decisive whether or not you do some masonry wall .
If the wood stove is to smoll , the masonry counter flow or bell will not help to much , just cheep  the heat longer. But if you surround the three-walled stove you will lose the direct radiant heat from stove .
You can make a masonry bell behind the stove , if residuale temperature of smoke is enough , other ways better to buy one biger with secondary air . Maybe , maybe a system heatig air will chenge something ...
At the  beginning  it is good to know , more exactly , the thermal necessities of the house .
 
george catalin
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Then your stove has no secondary air . Because is a metal stove , you can add secondary air tube to obtain secondary combustion with gasification .
But this modification will  increase to small  the power of stove , the combustion will be more clean .
Is good to do for stove that have power enough to heat whole house , which is not the case here .
I don't want to disappoint you, but, whatever you do willnot  double the power of the stove, as you say it is necessary .
 
pollinator
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thomas rubino wrote:
Yes, red clay bricks definitely have enough mass.
They are used in masonry stoves and more important in a rocket mass heater that utilizes a vertical brick bell.  



Gabe.
Fire bricks.... red clay bricks.... bricks bricks and more bricks....   But not all bricks will work for your application.

i think the bricks that thomas is speaking of are not the same "common" red clay bricks that are used on the outside of houses nor the type that are used in garden or landscaping applications.

i am pretty sure that the 'fire' bricks that are used in rocket mass heater applications are special purpose.  they are larger and much lighter than the other more common types.

if you do decide to build any 'walls' around the wood stove... i would suggest mimicking the Rumford fireplace angles.... like wide spread wings to mostly help reflect the radiant heat into the room.

Most of your heat loss is vertically up and away through the pipe.... Not sure how you could recapture some of this or help direct it into the room on its way up and away.  Maybe two small fans hung from the ceiling (or otherwise stationed) that would blow across the stovepipe and into the room or towards the corridors where the heat needs to be moved.  in my mind this would pull the heat off of the pipe and into the room.  Not sure if thermodynamics would then force the rising gases to transfer significantly more heat into the metal...or just a continued slow transfer would happen.   One caution.... you should have the fans turned off for the first 10-30 minutes until the stovepipe is hot.... or it could mess up the draw and cause backup or smoke to enter your room/house.

Peace
 
george catalin
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You can consider three types of stoves : metal  one , masonry wood stove and rocket mass stove .
A very good metal stove is expensive also , but do not take big space like other two . Also no have mass heater , which means that a more wood supply is required more often .
Masonry wood stove can heat whole house but need more space than metal one . Also can have panoramic glass , secondary air , combustion with gazeification , bell or counter flow , or both , water heat exchanger , and can be done vertically . But it is the heaviest stove of all for the same power end also , the hardest to build .
Rocket mass stove is cheaper than other two , good combustion end also can be done vertically , with bell or counter flow , and water heater exchanger . Also take more space than metal one .
Is your choise .
Best wishess .
 
george catalin
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C. E. Rice wrote:


i am pretty sure that the 'fire' bricks that are used in rocket mass heater applications are special purpose.  they are larger and much lighter than the other more common types.

Peace


Yes , dense refractory bricks have the ability to store the most heat
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pollinator
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We built a "hybrid" masonry stove starting with a wood stove for the fire box. You can check it out here, at http://geopathfinder.com/Masonry-Stove.html
In a previous home we had built a "real" masonry wood heater, complete with a warming bench, a puzzle chamber of flue paths, the whole 9 yards. The current hybrid stove works as well and was waaaay easier to construct.
 
george catalin
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Ok , but first , you have an entire plant there , second , you have an metal wood stove with masonry recovery .
Did your stove can heat wole house or almoust ?
How many degrees are there at the exit of stove ?
How many degrees are on the face of recovery ?
Thanks .
 
Gabe Smith
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Larisa Walk wrote:We built a "hybrid" masonry stove starting with a wood stove for the fire box. You can check it out here, at http://geopathfinder.com/Masonry-Stove.html
In a previous home we had built a "real" masonry wood heater, complete with a warming bench, a puzzle chamber of flue paths, the whole 9 yards. The current hybrid stove works as well and was waaaay easier to construct.



Wow! That is impressive, and I've only just taken a cursory look! I'm going to have to read through the whole blog closer, thank you so much for the link!
 
george catalin
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Dear lady Larisa , you did great  work . I do not know if in your  government help you to obtein more green energy . Hear more words than help .
I also bought water heater solar panel that is working 12 months per year , 1000 litres puffer two coils with 200 litres boiler inside , but not sollar panel for energy because I do not trust in their quality , and with help from government can buy just for few bulbs ,and I have electrical boiler that needs minimum 10KW .
Maibe in a future something will change . I am waiting for natural gas plant to instal gas boiler . If we cut everiday the forest , our grandchildren will see trees in a photos only .
Thanks for informations .
Have a good days .
 
gardener
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You already said your stove was undersized, so yes .... consider a new stove.  An an alternative solution for the mass, you may consider checking out a supplier of stone for granite counter tops.  Sometimes a "second"  can be obtained cheaply and would look great.
 
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